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Chemical element, symbol Tm and atomic number 69 / From Wikipedia, the free encyclopedia

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Thulium is a chemical element; it has symbol Tm and atomic number 69. It is the thirteenth and third-last element in the lanthanide series. Like the other lanthanides, the most common oxidation state is +3, seen in its oxide, halides and other compounds; however, the +2 oxidation state can also be stable. In aqueous solution, like compounds of other late lanthanides, soluble thulium compounds form coordination complexes with nine water molecules.

Quick facts: Thulium, Pronunciation, Appearance, Standard ...
Thulium, 69Tm
Pronunciation/ˈθjliəm/ (THEW-lee-əm)
Appearancesilvery gray
Standard atomic weight Ar°(Tm)
Thulium in the periodic table


Atomic number (Z)69
Groupf-block groups (no number)
Periodperiod 6
Block  f-block
Electron configuration[Xe] 4f13 6s2
Electrons per shell2, 8, 18, 31, 8, 2
Physical properties
Phase at STPsolid
Melting point1818 K (1545 °C, 2813 °F)
Boiling point2223 K (1950 °C, 3542 °F)
Density (near r.t.)9.32 g/cm3
when liquid (at m.p.)8.56 g/cm3
Heat of fusion16.84 kJ/mol
Heat of vaporization191 kJ/mol
Molar heat capacity27.03 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1117 1235 1381 1570 (1821) (2217)
Atomic properties
Oxidation states0,[3] +1,[4] +2, +3 (a basic oxide)
ElectronegativityPauling scale: 1.25
Ionization energies
  • 1st: 596.7 kJ/mol
  • 2nd: 1160 kJ/mol
  • 3rd: 2285 kJ/mol
Atomic radiusempirical: 176 pm
Covalent radius190±10 pm
Color lines in a spectral range
Spectral lines of thulium
Other properties
Natural occurrenceprimordial
Crystal structure hexagonal close-packed (hcp)
Hexagonal close packed crystal structure for thulium
Thermal expansionpoly: 13.3 µm/(m⋅K) (at r.t.)
Thermal conductivity16.9 W/(m⋅K)
Electrical resistivitypoly: 676 nΩ⋅m (at r.t.)
Magnetic orderingparamagnetic (at 300 K)
Molar magnetic susceptibility+25500×10−6 cm3/mol (291 K)[5]
Young's modulus74.0 GPa
Shear modulus30.5 GPa
Bulk modulus44.5 GPa
Poisson ratio0.213
Vickers hardness470–650 MPa
Brinell hardness470–900 MPa
CAS Number7440-30-4
Namingafter Thule, a mythical region in Scandinavia
Discovery and first isolationPer Teodor Cleve (1879)
Isotopes of thulium
Main isotopes[6] Decay
abun­dance half-life (t1/2) mode pro­duct
167Tm synth 9.25 d ε 167Er
168Tm synth 93.1 d β+ 168Er
169Tm 100% stable
170Tm synth 128.6 d β 170Yb
171Tm synth 1.92 y β 171Yb
Symbol_category_class.svg Category: Thulium
| references

In 1879, the Swedish chemist Per Teodor Cleve separated from the rare earth oxide erbia another two previously unknown components, which he called holmia and thulia; these were the oxides of holmium and thulium, respectively. A relatively pure sample of thulium metal was first obtained in 1911.

Thulium is the second-least abundant of the lanthanides, after radioactively unstable promethium which is only found in trace quantities on Earth. It is an easily workable metal with a bright silvery-gray luster. It is fairly soft and slowly tarnishes in air. Despite its high price and rarity, thulium is used as the radiation source in portable X-ray devices, and in some solid-state lasers. It has no significant biological role and is not particularly toxic.

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